1. Field of the Invention
The present invention generally relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus equipped with a paper feed roller for conveying paper.
2. Background Information
A thermal transfer printer as an example of known image forming apparatuses. The structure of a conventional thermal transfer printer will be described through reference to FIGS. 15 to 18.
Such conventional thermal transfer printer is generally equipped with a paper guide, to which a paper cassette is inserted. As shown in FIG. 17, paper 130 can be picked up with a paper feed roller 125 from that paper cassette 108 that inserted in the paper guide 106. As shown in FIG. 16, a middle separator wall 106a is provided to the lower paper guide 106, on the center line of the width of the paper feed roller 125, so as to be opposite the paper feed roller 125. Two separator walls 106b are also provided to the lower paper guide 106, one on each side of the middle separator wall 106a. As shown in FIG. 15, the middle separator wall 106a is the same height as the two separator walls 106b on the sides.
Also, as shown in FIG. 16, two guide components 108a that have a convex, round shape and serve as positional guides during paper feed are provided a predetermined distance apart to the paper cassette 108. The width Wc between the two inner lateral edge components of the paper cassette 108 in the N2 direction of FIG. 16 is set to be greater by X on each side than the width Wp of the paper 130, so that the edges of the paper 130 will not be damaged when the paper 130 is put into the paper cassette 108. Accordingly, there may be times when the paper 130 is placed in the paper cassette 108 in a skewed orientation relative to the paper feed direction (the direction of the arrow C2 in FIG. 16).
As shown in FIG. 17, the thermal transfer printer is further provided with a paper lifting member 109, which is attached to the paper cassette 108 so as to be pivotable about a paper lifting member support shaft 109a. A lifting lever 131 is attached so that the paper lifting member 109 will be pressed toward the paper feed roller 125 (upward) by a pressing means (not shown).
Next, the manner in which paper is fed in a conventional thermal transfer printer will be described through reference to FIGS. 17 and 18. During the paper feed operation, as shown in FIG. 17, the paper 130 is conveyed by the paper feed roller 125 in the paper feed direction (the direction of the arrow C2 in FIG. 17). At this time, a thermal head of the thermal transfer printer is pivoted in a direction away from the paper 130 while the paper 130 is being supplied (that is, while printing is not in progress).
When the paper feed roller 125 rotates in the direction the arrow H2 to convey the paper 130 in the paper feed direction, a paper feed force P4 is transmitted to the paper 130 as shown in FIG. 18. The center position of this paper feed force P4 is the center position of the width of the paper feed roller 125. Also, as a result of the paper 130 being conveyed, a load P5 is generated between the paper 130 and the middle separator wall 106a and the two separator walls 106b on the sides, which are in contact with the paper 130. The center of this load P5 is the center of the width of the separator wall 106a. Here, since the middle separator wall 106a is provided in the middle of the width of the paper feed roller 125 (or the center of the paper feed force P4), and the two separator walls 106b on the sides are provided symmetrically with respect to the middle separator wall 106a, the line of action of the paper feed force P4 is the same as the line of action of the load P5. Therefore, no rotational force is generated with respect to the paper 130.
However, as shown in FIG. 18, when the paper 130 is placed in the paper cassette 108 in a skewed orientation relative to the paper feed direction (the direction of the arrow C2 in FIG. 18), the combined force of the paper feed force P4 and the load P5 conveys the paper 130 in the paper feed direction in the skewed orientation.
As a result, when the paper 130 is conveyed in the paper feed direction, it is difficult to convey the paper 130 along the guide components 108a of the paper cassette 108. This results in variance in the width direction position of the paper 130 being fed.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming apparatus that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.